Polyanionized Rocksalt Cathodes for High-Voltage Cycling Stability
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Solution Overview
Problem
Existing lithium-ion battery cathodes face challenges in achieving high energy density and cycling stability due to lattice oxygen loss and structural instability at high voltages, particularly in Co/Ni-free disordered rocksalt cathodes, which require partial polyanionization to stabilize the lattice and suppress oxygen diffusion.
Innovation Solution
A family of lithium-excess, manganese-rich cathodes with spinel-like cation ordering and partial polyanionization, incorporating XO4 polyanion units into a Li-M-O rocksalt structure, where M is Mn or Fe, and X is P, Si, or B, to form Li2+u-vM2-u[XO4]xO4(1-x), stabilizing the lattice and enhancing cycling stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high upper cutoff voltages (4.8 V vs. Li/Li+) are used to achieve high energy densities, then energy density is improved, but lattice oxygen loss and structural instability occur
Solution Approach 1:
XO4 polyanion units (where X=P, Si, S, B) are introduced as intermediary structural components within the rocksalt cathode framework. These polyanion units act as mediators that stabilize the lattice structure at high voltages, preventing oxygen loss while allowing the cathode to operate at 4.8 V vs. Li/Li+ for high energy density
Solution Approach 2:
The cathode employs a composite structure combining rocksalt Li-M-O framework with embedded XO4 polyanion units. This composite architecture integrates the high energy density characteristics of rocksalt cathodes with the structural stability of polyanion compounds, achieving both high energy density and cycling stability
2Reliability
If polyanion units are incorporated to stabilize the lattice and suppress oxygen diffusion, then cycling stability is improved, but diffusion kinetics and capacity may be penalized
Solution Approach 1:
The cathode structure exhibits local quality variation where XO4 polyanion units are strategically distributed within the rocksalt framework. These localized polyanion regions provide structural stability and suppress oxygen diffusion, while the surrounding rocksalt regions maintain good Li+ diffusion kinetics, achieving a balance between stability and productivity
3Adaptability or versatility
If Co and Ni are eliminated from oxide cathodes to improve scalability, then resource availability is improved, but achieving high energy densities becomes more difficult
Solution Approach 1:
The cathode employs parameter changes in composition (Li-excess, manganese-rich stoichiometry with Li2+u-vM2-u[XO4]xO4(1-x)) and structure (rocksalt with spinel-like cation ordering and partial polyanionization) to achieve high energy densities using only abundant Li, Mn, and Fe elements, eliminating dependence on scarce Co and Ni
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The cathodes achieve high energy densities above 900 Wh kg−1 and improved cycling stability, maintaining capacity and energy retention over 100 cycles, with compositions like Li1.67Mn1.5P0.17O4 showing 72% capacity and 71% energy density retention.
Implementation Method 1
Oxide ions within the polyanion group are strongly bound to X via covalent bond such that long-range percolation of lattice oxygen diffusion/loss is suppressed
Implementation Method 2
This often triggers the participation of oxygen anion redox
Data Source
AI summary
Disclosed herein is a cathode for a lithium-ion battery having a formula:Li2+u-vM2-u[XO4]xO4(1-x) where, 0≤u≤1, 0≤v≤2 and 0≤x≤1, wherein M is a transition metal element of manganese or a mixture of manganese and iron, and X is an element of phosphorus, silicon, sulfur, boron, or a mixture of these elements.